One of the most important requirements of a next generation wireless communication system is to support a required high data rate. For this, various techniques such as multiple input multiple output (MIMO), cooperative multiple point transmission (CoMP), relay, etc., have been under research, but the most fundamental and reliable solution is to increase a bandwidth.
However, a frequency resource is in a saturation state at present, and various schemes are partially used in a wide frequency band. For this reason, in order to ensure a broadband bandwidth to satisfy a required higher data rate, a system is designed to satisfy a basic requirement which requires separate bands capable of operating respective independent systems, and a carrier aggregation (CA) is introduced. In concept, the CA aggregates a plurality of bands into one system. In this case, each band that can be independently managed is defined as a component carrier (CC).
To support growing transmission capacity, the 3GPP LTE or the 802.16m has recently expanded its bandwidth to 20 MHz or higher. In this case, a wideband is supported by aggregating one or more CCs. For example, if one CC corresponds to a bandwidth of 5 MHz, four carriers are aggregated to support a bandwidth of up to 20 MHz.
As such, a plurality of CCs are used in the carrier aggregation system. In this case, a user equipment (UE) may have the following features: 1) a CC for receiving downlink control information from a base station (BS) may be set differently from a CC for receiving downlink data; or 2) links of a CC for receiving downlink control information and a CC for transmitting an uplink signal may follow a link relation different from a link determined in the existing LTE. Such a scheduling method is called cross-carrier scheduling. The cross-carrier scheduling can be called downlink cross-carrier scheduling in the former caser, and can be called uplink cross-carrier scheduling in the latter case.
A method of applying the uplink cross-carrier scheduling has not been defined yet for a case where the cross-carrier scheduling is applied to the carrier aggregation system.